Multiple Evolutionary Pathways to Host Adaptation in the Fall Armyworm

During the over 300 million years of co-evolution between herbivorous insects and their host plants, a dynamic equilibrium of evolutionary arms race has been established. However, the co-adaptation between insects and their host plants is a complex process, often driven by multiple evolutionary mechanisms. We found that various lepidopteran pests that use maize as a host exhibit differential adaptation to the plant secondary metabolites, benzoxazinoids (BXs). Notably, the Spodoptera genus, including Spodoptera frugiperda (fall armyworm) and Spodoptera litura (cotton leafworm), demonstrate greater tolerance to BXs compared to other insects. Through comparative transcriptomic analysis of the midgut, we identified four candidate genes potentially involved in BXs detoxification in S. frugiperda. Subsequently, we confirmed two UGT genes, Sfru33T10 and Sfru33F32, as key players in BXs detoxification using CRISPR/Cas9 gene-editing technology. Phylogenetic analysis revealed that Sfru33T10 evolved independently within the Noctuidae family and is involved in the glycosylation of HDMBOA, while Sfru33F32 evolved independently within the Spodoptera genus and functions as a key detoxification enzyme responsible for the glycosylation of both DIMBOA and HMBOA. Our study demonstrates that the UGT gene family plays a crucial role in the adaptation of noctuid insects to maize, with multiple independent evolutionary events within the Noctuidae family and the Spodoptera genus contributing significantly to host adaptation. To investigate the gene expression profiles of FAW under different feeding conditions, fourth-instar larvae of each species were fed fresh maize leaves (W22) for 24 hours. Larvae fed with artificial feed (AF) served as controls. After the feeding period, midguts were rapidly dissected and frozen in liquid nitrogen for further analysis. Each treatment consisted of three biological replicates, with five midguts pooled per replicate.